Retardation films are used in liquid crystal display devices in order to enlarge the view angle and improve contrast. In recent years, thinning of liquid crystal panels and improvements of liquid crystals in liquid crystal cells have been made to realize for example high response speed, light weight, and reduced manufacturing costs of liquid crystal displays, requesting further thinning of the retardation films. In addition, demands for thinner retardation films are high as means to achieve cost reductions through high-speed production and elongation of the retardation film. As a result, much higher performance is required for retardation films; for example, they are required to exhibit, even if the film thickness is extremely small, high retardation performance and mechanical strength high enough to cause no problem in handling. Further, the distance between the backlight and polarizing plate decreases with decreasing thickness of the liquid crystal panel resulting in greater influence of heat generated from the backlight unit. Accordingly, retardation films are required to exhibit, even when they are made thin, superior durability compared to conventional ones.
Films containing cellulose derivatives have been widely used as retardation films because of their excellent moisture permeability, a property which is required when manufacturing a polarizing plate. In order to increase the retardation of such cellulose derivative-containing films, techniques have been proposed wherein cellulose esters having a low total degree of acyl substitution are used; compounds having a retardation development effect are added to films; and the films are stretched (see, e.g., PTL 1 to 3).